1. Field of the Invention
The present invention relates to an alarm information transfer system in a digital transmission device.
2. Description of the Related Art
In recent years, there are various kinds of alarm information for notifying fault found in devices, circuits and the like, due to improvement of functions of the devices, the circuits composing the devices, and the like.
Therefore, it is not sufficient to use a system in which only some of the units collect alarm information from other units. From the view point of reliability, it is desirable to use a system in which alarm information can be shared among each of the units.
FIG. 6 shows one example of the conventional alarm information transfer system to cover the above described demands.
In FIG. 6, reference numerals 1, 2 . . . n mean the plurality of alarm information transfer circuits, all of which are provided in one device. Each of the alarm information transfer circuits has the same structure.
One of the alarm information transfer circuits is used as a master unit 1, and others are used as slave units 2 to n. Hereinafter, alarm information transfer units are referred to as units.
A master unit 1 supplies a clock CLK and a flame pulse FP. All slave units 2 to n receive alarm information collected from a corresponding alarm information source 40 and store it in the data memory 10. The alarm information source 40 of CPU generates alarm information, referred to as alarm information.
The slave units 2 to n convert several kinds of alarm information stored in the data memory 10 to serial data in a predetermined time, according to unit numbers set by an ID setting circuit 50 in advance, and transfer the data to the master unit 1.
The serial data is multiplexed in a time-sharing manner, so that alarm information from each of the slave units 2 to n is collected in the master unit 1. The collected data is stored in the data memory 10 of the master unit 1, and referenced successively under the control of CPU 40 of the master unit 1.
In the conventional system, the master unit 1 and other slave units 2 to n are defined individually, to transfer the alarm information data from the slave units 2 to n to the master unit 1, unilaterally.
Thus, the alarm information from other units can not be referred on from the CPU 40, to the other slave units 2 to n. Accordingly, a problem is that the overall system can not deal with a fault indicated by the alarm rapidly.
Further, only the master unit 1 has the supply source of clock CLK and flame pulse FP in the conventional system, so that the clock CLK and flame pulse FP can not be supplied from other slave units, when the clock CLK or the flame pulse FP supplied from the master unit 1 are disconnected. Therefore, another problem is that all communications are stopped when the clock CLK or the frame pulse FP supplied from the master unit 1 is disconnected.